David Roland-Holst the report's author and an adjunct professor at UC-Berkeley, said, "Our report makes clear the most expensive thing we can do is nothing."

Roland-Holst said that while multiple studies have projected the economic impact of taking action to reduce global warming emissions, this is the first to comprehensively assess the potential costs of climate risk and review opportunities for strategic adaptation.

He said real estate and insurance, taken together, represent the largest economic climate risk for California, yet they are the least studies to date.

The report finds that the state has $4 trillion in real estate assets, of which $2.5 trillion are at risk from extreme weather events, the potential rise in sea levels and wildfires.

Roland-Holst said the annual price tag for the economic climate risk ranges wildly from $300 million to $3.9 billion over this century, depending on how warm the world gets.

He said if no action is taken in the face of rising temperatures, six additional sectors, including water, energy, transportation, tourism and recreation, agriculture and public health, would together incur bens of billions per year in direct costs, and even higher indirect costs, and expose trillions of dollars of assets to collateral risk.

The study was funded by Next 10, a Palo Alto-based nonpartisan nonprofit organization.

The group's founder, venture capitalist F. Noel Perry, said, "The scale of climate risk over the coming decades dwarfs today's financial crisis and will long outlive it. It is up to responsible leadership to protect the public interest."

Roland-Holst said the report finds that effective responses to climate change, including mitigation to prevent the worst impacts, can be carried out at a fraction of the long-term cost of inaction.

He said California must act without delay to expand the technical assessment of climate risk and policy options, begin to re-deploy existing resources for infrastructure renewal and replacement and provide private incentives to promote long-term adaptation, including investments for climate security and energy independence.

Roland-Holst said he believes directing public spending toward a more climate-friendly infrastructure can stimulate local job creation and complimentary private investments.

He said private sector growth can be further accelerated with investment incentives and other promotion for energy efficiency and technologies for climate adaptation.